It has been a nice, warm, and very sunny day today. It seems a shame to waste such a day, so I got out for a bit after my last class of the day. As it happens, there's a nice arboretum just a few minutes' drive away, so I went to have a look around.
There were quite a few lovely specimens of
Homo sapiens coedicus wandering about the area. As best I could tell, they had all shed their heavy winter pelages for somewhat less insulative coverings.
There is a low-lying, swampy area at one end of the arboretum, and a couple of hundred yards up a gentle slope is an artificial pond. There were some kids excitedly talking about a "huge turtle," so I went to investigate. As it turned out, a Snapping Turtle (
Chelydra serpentina) was making its way out of the swamp, apparently heading for the pond. I warned the kids not to mess with the turtle, as snapping turtles are quick to defend themselves when on land (they tend to be surprisingly timid when in the water though), and can give a nasty bite. Supposedly, an adult snapping turtle can amputate a person's finger with a bite, though I know of no actual instances of that happening. (Though I once had one take a chunk out of a leather boot I had been wearing at the time. I'm just as glad it wasn't my foot ...)
This particular turtle certainly wasn't fully grown, but it was more than large enough to have delivered a painful bite. Rather than risk someone else coming across the turtle and perhaps harming it -- and/or being harmed by the turtle -- I decided it would be best to speed it to its destination. So I showed the kids how to safely pick up a snapping turtle and carried it to the pond. They seemed impressed.
On the other hand, I sometimes worry about what kind of precident that sort of thing sets. I remember a General Zoology course I taught once in North Carolina. I took the students outside whenever possible, and would catch snakes, lizards, frogs, fishes, crayfishes, insects, etc. to show to them. This was all well and good, because I certainly wanted to show the students how interesting the animals in question were, and to dispel some negative stereotypes.
However, one young woman caught a large Fowler's Toad (
Bufo fowleri) and announced that she was going to keep it as a pet. I told her that I really wished she wouldn't, and that it'd be better to leave the animal in its natural habitat. "But you catch animals all the time," she protested. I pointed out that I catch animals to show to students, and that afterwards I'm always very careful to return them to exactly where I found them.
Anyway, some crocuses and
Forsythia were just coming into bloom near the main entrance to the main entrance to the arboretum, as was a lovely Star Magnolia (
Magnolia stellata).
But those don't really count, as far as I'm concerned, since they're non-native cultivars.
Speaking of which, I noticed that the name tag on one of the trees identified it as an Eastern Redcedar (
Juniperus virginiana). That's all well and good, except that the tree was quite clearly a
Western Redcedar (
Thuja plicata), a species with a distinctly-different leaf shape and growth form. I'll have to make a mental note to find somebody in charge of the arboretum and mention that to them.
After releasing the snapping turtle, I wandered around the pond for awhile. Water Striders (genus
Aquarius, most likely) "skated" across the surface.
A water molecule is, overall, electrically neutral. But because the electrons are not "shared" equally between the two hydrogen atoms and the oxygen atom that make up a water molecule (the oxygen tends to "hoard" the electrons), a water molecule is
polar. That is, the oxygen atom has a slight negative charge (because the negatively-charged electrons spend proportionately more time in the vicinity of the oxygen atom) and the two hydrogen atoms each have slightly positive charges (because the electrons spend proportionately less time in their vicinity and so can't
quite balance the positive charges of the hydrogen atoms' protons).
As a result of the polar nature of water molecules, they tend to be strongly attracted to each other. That's because the partially-negative oxygen atom of one water molecule is attracted to the partially-positive hydrogen atoms of nearby water molecules.
Within a body of water, any individual water molecule will feel no net force due to these attractions, because each molecule is being attracted by surrounding molecules in every direction. And so the forces exerted by all the surrounding molecules cancel out. But for a water molecule at the
surface, things are different.
Since a water molecule at the surface is not attracted to the air molecules above it, but
is attracted by the water molecules to its sides and beneath it, a net downward force results. This causes the water molecules at the surface to be pulled together, relative to water molecules inside the body of water. Because the water molecules at the surface are thus under tension, we say that the water has
surface tension. The surface tension resists penetration, and so anything that's light-enough can literally walk on water.
Water striders have
hydrophobic (water-repelling) "hairs" on their legs. Since the water molecules don't stick to their legs, water striders can walk on water. You can, if you're interested, calculate whether or not an animal can walk on water. It's a function of the animal's weight and the amount of its body that's touching the surface of the water.
The actual formula is:
.
T represents the surface tension, which resists the animal breaking through the surface of the water. (That's 0.073 Newtons/meter in freshwater.) The letter
p represents the animal's density (in kilograms per cubic meter). The letter
l represents the length (perimeter) of the animal's body that's touching the water surface, in meters. (The more of the animal's body that's touching the water surface, the more its weight is spread out, and so the less likely it is to break through the surface tension.) The
g represents the force exerted by gravity, which is attempting to pull the animal through the surface tension.
If you do the calculations and
Je is greater than 1, the animal can walk on water. Oh, what
is Je? It's called the "Jesus number." If your Jesus number is greater than 1, you can walk on water.
Why can't large animals walk on water? Because mass (weight) is a cubic function, but surface area is only a square function. This means that as animals grow larger, their weight increases far faster than does their surface area. So only very small animals can possibly have feet that are large-enough relative to their weights to support them on water.
Anyway, lots of water striders were "skating" across the pond. Animals are mostly made of water and organic molecules, and most organic molecules are polar. This means that for a very small animal, like your average insect, water can be very-much like glue. Water striders don't stick to water because of their water-repellent coatings, but most other insects aren't so lucky. So for most other insects, falling onto the surface of a body of water is very much like what we'd experience falling into a vat of warm tar -- escape is all but impossible. Water striders are predators, and they cruise about the surface of ponds and lakes, in search of unfortunate insects that get trapped on the surface.
There were lots of Whirligig Beetles (probably genus
Gyrinus) scooting about on the surface of the pond as well. Like the water striders, they have waterproof coatings, and so can move on the water's surface without sticking to it. One thing that makes them interesting is that they have divided eyes -- one half of each eye projects above the water's surface, which allows them to scan for potential predators, while the other half of each eye projects below the water's surface and scans for prey or for predators approaching from below. (The beetles dive for prey.)
Like water striders, whirligig beetles can push against the water's surface to "skate" along, much like an ice skater does.
Speaking of beetles and surface tension, my favorite example is
Rove Beetles (family Staphylinidae). Some rove beetles have a really neat trick, should they happen to fall onto some water. To escape the sticky deathtrap, the beetle secretes a
surfactant from openings in its abdomen.
A surfactant is a substance that reduces surface tension. (Detergents are surfactants.) When a rove beetle secretes surfactant from its abdomen, this lessens the surface tension behind it, but not in front of it. This creates an unbalanced force and the beetle is propelled by it across the surface of the water. The beetle can keep this up until it runs out of surfactant; hopefully, it'll hit dry land before that happens.
Painted turtles (
Chrysemys picta) were swimming in the pond and basking on logs that protruded from the water. Green Frogs (
Rana clamitans) were sitting on the shore or floating in the shallow water near shore.
I wandered down to the swampy area, and several male Red-Winged Blackbirds (
Agelaius phoeniceus) were
calling from the dead stems of last year's Cat-Tails (
Typha latifolia).
Red-wings are interesting insofar as they have very different breeding behavior from most other songbirds. Males arrive in swampy areas during the early Spring and begin setting up territories. Swamps tend to have lots of food available for songbirds, and a good territory can easily support several nests. What's more, in a good territory, a female can easily find enough food to feed her offspring, even without help from her mate.
Consequently, a male who manages to secure an especially choice territory may have 5, 6 or even more females nesting in his territory. (Some especially successful males have had as many as
15.) He mates with each female in his territory and then zealously defends the territory against all intruders. Other than defending against intruders, he plays little or no role in raising his offspring.
A pair of White-Breasted Nuthatches (
Sitta carolinensis) flew past and alighted on a nearby tree trunk. They have this neat habit of landing near the top of a tree and then methodically moving down the tree trunk (upside-down), while prying the bark aside in search of hidden insects.
In the wet ground near the edge of the swamp, some Eastern Skunk Cabbage (
Symplocarpus foetidus) was just coming into bloom, filling the nearby air with its distinctive stench. (It isn't called "Skunk Cabbage" for nothing!) The plant begins to bloom in the very early Spring, often while snow is still on the ground. The combination of its heat-absorbing dark coloration and its very high metabolic rate (for a plant) means that it can actually melt the snow around it. The scent is somewhat like that of rotting meat, which attracts the flies that pollinate its flowers.
There was some movement in the cattails, and a Garter Snake slid into view. It froze when I moved to get a better look at it, but eventually continued on its way when I made no threatening movements.
Some sudden movement in the water turned out to be a Muskrat (
Ondatra zibethicus). It surfaced, grabbed a cattail stem, and then dragged it under the water. Presumably, it then headed to its den to eat in peace.
Something was thrashing about in the dry leaves nearby; it turned out to be an Eastern Gray Squirrel (
Sciurus carolinensis). Despite the common name, this squirrel was actually jet black.
Melanism is the exact opposite of
albinism. A "melanistic" animal is one that produces an overabundance of the dark pigment
melanin and so has very dark skin and feathers (if a bird) or fur (if a mammal).
Black squirrels are actually fairly common in parts of the American Midwest and Northeast, and the dark coloration may be adaptive in colder climates. (It may help them absorb solar radiation more efficiently.) I've heard that black squirrels are actually tourist attractions in some city parks. (Battle Creek, Michigan has a large population of black squirrels, for instance.)
As I moved up and into the woods above the swamp, I noted that a number of deer exclosures had been set up. These prevent the hooved locusts from gobbling up virtually every plant on the ground. What we
really need around here are more coyotes, cougars and wolves!
There was a
lot more green on the ground in the deer exclosures than there was outside of them. I noticed some Trout Lily (
Erythronium americanum) just coming into bloom in one of the exclosures. I may have to return this weekend with my trusty camera.
Some Common Blue Violets (
Viola sororia) were also coming into bloom. If the weather continues like this, this weekend might be an excellent time to begin the Springtime routine of tramping through the nearby woodlands at every available opportunity, in search of Spring ephemerals.
When I got back to the lake in the main part of the arboretum, a Tree Swallow (
Tachycineta bicolor) was zooming low over the water, dipping its beak downward every now and again to take a sip.
A Bullfrog (
Rana catesbeiana) was floating in the water near the shore. It's entirely possible that the frog could have caught and eaten the swallow, if the bird had been sufficiently unwary. (Not that I think the frog's speed and reflexes would have been up to catching a swallow on the wing.) Bullfrogs have been known to (somehow) catch and eat small snakes, mice, and even birds.
Some Song Sparrows (
Melospiza melodia) were
calling from the nearby trees. A brilliantly-red Northern Cardinal (
Cardinalis cardinalis) was
calling as well.
Some Blue Jays (
Cyanocitta cristata) were calling, too. For whatever reasons, a lot of people don't like blue jays, but they rank as one of my favorite bird species; they're not only strikingly beautiful, they're remarkably intelligent. Most people who live in the eastern half of the U.S. are probably familiar with the blue jay's "jay! jay! jay!"
alarm call, but few people realize they actually have lovely
singing voices.
As an aside, this might be surprising to some people given that blue jays are well-known for their ability to coexist with humans, but in the early days of this nation, blue jays were noted for their remarkable
shyness and their reluctance to live anywhere near human settlements. (Evidently, in the intervening years, they've gotten over it.) This was such a noteworthy trait of blue jays that people who lived out in the country, well away from any sizable settlements, were called "jays." That's supposedly where the expression "jaywalking" comes from -- since, presumably, only a hick (a "jay") wouldn't know how to cross a street properly.
Surprisingly, in one of the trees near the pond, a Gray Treefrog was calling. It's awfully early in the season, but evidently this one was getting an early start. This one was
Hyla chrysoscelis, Cope's Gray Treefrog. Cope's gray treefrog and the Common Gray Treefrog (
Hyla versicolor) are known as "cryptic species" because, though they often occupy the same area and are impossible to tell apart by sight, they are separate species that do not interbreed. Aside from counting their chromosomes, the only way to tell them apart is by listening to their calls. The call of
Hyla chrysoscelis is a
fast trill; the call of
Hyla versicolor is
slower.
Yup, Spring is definitely springing!
Cheers,
Michael
Spring is Sprung!
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